The goal of this research project is the investigation of the hormonal regulation of salt and water balance and of blood pressure, from the point of view of circadian regulation. This research is carried out in normal subjects, in female volunteers on oral contraceptives and in patients with endocrine hypertension (Cushing's syndrome, primary aldosteronism, etc.). We sample blood for aldosterone, renin activity, cortisol, etc, at half-hourly intervals over a 25-26 hour span. We have been developing, in their theoretical and practical aspects, procedures of mathematical analysis, up to now not available in the literature. The goal of this analysis is objective identification of the periodicity and quantitative estimation of the periodic parameters, univariate or bivariate. The application of these methods, based on frequency and correlation analysis and on information theory and graph theory, is of considerable help in the interpretation of the experimental data. BIBLIOGRAPHIC REFEFENCES: Leenen, F. H., Galla, S. J., Redmond, D. P., Vagnucci, A. H., McDonald, R. H., Jr., amd Shapiro, A. P. Relationships of the renin-angiotensin-aldosterone system and sodium balance to blood pressure regulation in chronic renal failure of polycystic kidney disease. Metabolism, 24:589-603, 1975. Liu, T. S., Vagnucci, A. H., and Wong, A. K. C. Pattern recognition of endocrine hypertension by Karhunen-Loeve analysis of time series. Proceedings of International Conference on Systems, Man and Cybernetics, San Francisco, California, 1975.